• Half of all customers who purchased in the past twelve months subscribe to e-mail campaigns.
• E-mail buyers have a 77% annual repurchase rate, among the most loyal of any channel.
• Only 25% of your e-mail file bothers to click on at least one e-mail campaign, per year. The remaining 75% are inactive.
• Only 5% of your e-mail file buy something from your e-mail campaigns, on an annual basis.
• E-mail is what I call a "transition channel". It is the channel that your customers migrate to as they begin to rely upon catalog marketing less. After the customer buys from an e-mail campaign, the customer is likely to buy from your website, without attribution to any other marketing campaign.
• 80% of your e-mail purchasers buy merchandise on sale, or buy when free shipping is offered. As a result, your e-mail buyer file is over-populated with discount shoppers.
• When you offer full price merchandise via e-mail, you generate $0.05 per e-mail campaign.
• When you offer sale merchandise, or you offer free shipping, you generate $0.25 per e-mail campaign.
• Over time, you optimized e-mail performance based on the metrics you had available to you ... open rates, click-through rates, conversion rates. As a result, your optimization best practices resulted in a program that sale/promo customers love. Your customers are no longer interested in e-mail marketing unless there is a marketing promotion.

Source: Kevin Hillstrom’s MineThatData Blog